WORKERS AHEAD!
You are viewing the development documentation for the Apereo CAS server. The functionality presented here is not officially released yet. This is a work in progress and will be continually updated as development moves forward. You are most encouraged to test the changes presented.
To view the documentation for a specific Apereo CAS server release, please choose an appropriate version. The release schedule is available here.Duo Security Authentication
Duo Security is a two-step verification service the provides additional security for access to institutional and personal data.
Duo offers several options for authenticating users:
- a mobile push notification and one-button verification of identity to a smartphone (requires the free Duo Mobile app)
- a one-time code generated on a smartphone
- a one-time code generated by Duo and sent to a handset via SMS text messaging
- a telephone call from that will prompt you to validate the login request
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<dependency>
<groupId>org.apereo.cas</groupId>
<artifactId>cas-server-support-duo</artifactId>
<version>${cas.version}</version>
</dependency>
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implementation "org.apereo.cas:cas-server-support-duo:${project.'cas.version'}"
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dependencyManagement {
imports {
mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
}
}
dependencies {
implementation "org.apereo.cas:cas-server-support-duo"
}
Please note that support for Duo multifactor authentication that is based on the Duo's Web SDK and the embedded iFrame is deprecated and scheduled to be removed in the future. You should consider switching to the 'Universal Prompt' variant described in this document to avoid surprises in future upgrades.
Actuator Endpoints
The following endpoints are provided by CAS:
Multiple Instances
CAS multifactor authentication support for Duo Security allows multiple Duo providers to be configured with distinct ids each of which may be connected to a separate Duo Security instance with a different configuration. This behavior allows more sensitive applications to be connected to a Duo instance that has more strict and secure authentication policies.
For this behavior to function, separate unique ids of your own choosing need to be assigned to each Duo Security provider. Each provider instance is registered with CAS and activated in the authentication flows as necessary. The provider id need not be defined if there is only a single Duo instance available.
Account Profile Management
The integration with Duo Security is able to provide user device registration information to the account profile management feature in CAS. See this guide for better details.
User Account Status
If users are unregistered with Duo Security or allowed through via a direct bypass, CAS will query Duo Security for the user account apriori to learn whether user is registered or configured for direct bypass. If the account is configured for direct bypass or the user account is not registered yet the new-user enrollment policy allows the user to skip registration, CAS will bypass Duo Security altogether and shall not challenge the user and will also NOT report back a multifactor-enabled authentication context back to the application.
In recent conversations with Duo Security, it turns out that the API behavior has changed (for security reasons) where it may no longer accurately report back account status. This means even if the above conditions hold true, CAS may continue to route the user to Duo Security having received an eligibility status from the API. Duo Security is reportedly working on a fix to restore the API behavior in a more secure way. In the meanwhile, YMMV.
Health Status
CAS is able to contact Duo Security, on demand, in order to inquire
the health status of the service using Duo Security’s ping API.
The results of the operations are recorded and reported using health endpoint
provided by CAS Monitoring endpoints.
Of course, the same result throughout the Duo authentication flow is also used to determine failure modes.
Universal Prompt
Universal Prompt is a variation of Duo Multifactor Authentication that uses the Duo OIDC Auth API. This is an OIDC standards-based API for adding strong two-factor authentication to CAS. This option no longer displays the Duo Prompt in an iFrame controlled and owned by CAS. Rather, the prompt is now hosted on Duo’s servers and displayed via browser redirects. The response from Duo Security is passed to CAS as a browser redirect and CAS will begin to negotiate and exchange that response in favor of a JWT that contains the multifactor authentication user profile details.
Universal Prompt no longer requires you to generate and use a application key value. Instead, it requires a client id and client secret, which are known and taught CAS using the integration key and secret key configuration settings. You will need get your integration key, secret key, and API hostname from Duo Security when you register CAS as a protected application.
Non-Browser MFA
The Duo Security module of CAS is able to also support non-browser based multifactor authentication requests.
In order to trigger this behavior, applications (i.e. curl, REST APIs, etc) need to specify a special
Content-Type to signal to CAS that the request is submitted from a non-web based environment.
The multifactor authentication request is submitted to Duo Security in auto mode which effectively may
translate into an out-of-band factor (push or phone) recommended by Duo as the best for the user’s devices.
In order to successfully complete the authentication flow, CAS must also be configured with a method of primary authentication that is able to support non-web based environments such as Basic Authentication.
Here is an example using curl that attempts to authenticate into a service by first exercising
basic authentication while identifying the request content type as application/cas. It is assumed that the
service below is configured in CAS with a special multifactor policy that forces the flow
to pass through Duo Security as well.
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curl --location --header "Content-Type: application/cas" https://apps.example.org/myapp -L -u casuser:Mellon
Configuration
The following settings and properties are available from the CAS configuration catalog:
cas.authn.mfa.duo[0].bypass.groovy.location=
The location of the resource. Resources can be URLS, or files found either on the classpath or outside somewhere in the file system. In the event the configured resource is a Groovy script, specially if the script set to reload on changes, you may need to adjust the total number ofinotify instances.
On Linux, you may need to add the following line to /etc/sysctl.conf:
fs.inotify.max_user_instances = 256.
You can check the current value via cat /proc/sys/fs/inotify/max_user_instances.
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cas.authn.mfa.duo[0].bypass.rest.url=
The endpoint URL to contact and retrieve attributes. |
cas.authn.mfa.duo[0].duo-api-host=
Duo API host and url. This setting supports the Spring Expression Language. |
cas.authn.mfa.duo[0].duo-application-key=
The application key is a string, at least 40 characters long, that you generate and keep secret from Duo. This is a required setting for the WebSDK integration types. Leaving this setting as blank will activate the Universal Prompt option. You can generate a random string in Python with:import os, hashlib print hashlib.sha1(os.urandom(32)).hexdigest() This setting supports the Spring Expression Language. |
cas.authn.mfa.duo[0].duo-integration-key=
Duo integration key. This setting supports the Spring Expression Language. |
cas.authn.mfa.duo[0].duo-secret-key=
Duo secret key. This setting supports the Spring Expression Language. |
cas.authn.mfa.duo=
Activate and configure a multifactor authentication provider via Duo Security. |
cas.authn.mfa.duo[0].bypass.authentication-attribute-name=
Skip multifactor authentication based on designated authentication attribute names. |
cas.authn.mfa.duo[0].bypass.authentication-attribute-value=
Optionally, skip multifactor authentication based on designated authentication attribute values. |
cas.authn.mfa.duo[0].bypass.authentication-handler-name=
Skip multifactor authentication depending on form of primary authentication execution. Specifically, skip multifactor if the a particular authentication handler noted by its name successfully is able to authenticate credentials in the primary factor. |
cas.authn.mfa.duo[0].bypass.authentication-method-name=
Skip multifactor authentication depending on method/form of primary authentication execution. Specifically, skip multifactor if the authentication method attribute collected as part of authentication metadata matches a certain value. |
cas.authn.mfa.duo[0].bypass.credential-class-type=
Skip multifactor authentication depending on form of primary credentials. Value must equal the fully qualified class name of the credential type. |
cas.authn.mfa.duo[0].bypass.http-request-headers=
Skip multifactor authentication if the http request contains the defined header names. Header names may be comma-separated and can be regular expressions; values are ignored. |
cas.authn.mfa.duo[0].bypass.http-request-remote-address=
Skip multifactor authentication if the http request's remote address or host matches the value defined here. The value may be specified as a regular expression. |
cas.authn.mfa.duo[0].bypass.principal-attribute-name=
Skip multifactor authentication based on designated principal attribute names. |
cas.authn.mfa.duo[0].bypass.principal-attribute-value=
Optionally, skip multifactor authentication based on designated principal attribute values. |
cas.authn.mfa.duo[0].bypass.rest.basic-auth-password=
If REST endpoint is protected via basic authentication, specify the password for authentication. |
cas.authn.mfa.duo[0].bypass.rest.basic-auth-username=
If REST endpoint is protected via basic authentication, specify the username for authentication. |
cas.authn.mfa.duo[0].bypass.rest.headers=
Headers, defined as a Map, to include in the request when making the REST call. Will overwrite any header that CAS is pre-defined to send and include in the request. Key in the map should be the header name and the value in the map should be the header value. |
cas.authn.mfa.duo[0].bypass.rest.method=GET
HTTP method to use when contacting the rest endpoint.
Examples include |
cas.authn.mfa.duo[0].account-status-enabled=true
When set to |
cas.authn.mfa.duo[0].duo-admin-integration-key=
Duo admin integration key. This setting supports the Spring Expression Language. |
cas.authn.mfa.duo[0].duo-admin-secret-key=
Duo admin secret key. This setting supports the Spring Expression Language. |
cas.authn.mfa.duo[0].failure-mode=CLOSED
The failure mode policy for this MFA provider. The authentication policy by default supports fail-closed mode, which means that if you attempt to exercise a particular provider available to CAS and the provider cannot be reached, authentication will be stopped and an error will be displayed. You can of course change this behavior so that authentication proceeds without exercising the provider functionality, if that provider cannot respond. Each defined multifactor authentication provider can set its own failure mode policy. Failure modes set at this location will override the global failure mode, but defer to any failure mode set by the registered service. Available values are as follows:
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cas.authn.mfa.duo[0].id=
The identifier for the multifactor provider. In most cases, this need not be configured explicitly, unless multiple instances of the same provider type are configured in CAS. |
cas.authn.mfa.duo[0].name=
The name of the authentication handler used to verify credentials in MFA. Remember that if you have more than one authentication handler of the same type, the names must be defined uniquely for each authentication scheme. Failing to do so may force CAS to not register authentication handlers with a duplicate name. |
cas.authn.mfa.duo[0].order=MAX_VALUE
The order of the authentication handler in the chain. |
cas.authn.mfa.duo[0].rank=
At times, CAS needs to determine the correct provider when step-up authentication is required. Consider for a moment that CAS already has established an SSO session with/without a provider and has reached a level of authentication. Another incoming request attempts to exercise that SSO session with a different and often competing authentication requirement that may differ from the authentication level CAS has already established. Concretely, examples may be:
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cas.authn.mfa.duo[0].registration-url=
Link to a registration app, typically developed in-house in order to allow new users to sign-up for duo functionality. If the user account status requires enrollment and this link is specified, CAS will redirect the authentication flow to this registration app. Otherwise, the default duo mechanism for new-user registrations shall take over. |
cas.authn.mfa.duo[0].trusted-device-enabled=
Indicates whether this provider should support trusted devices. |
Configuration Metadata
The collection of configuration properties listed in this section are automatically generated from the CAS source and components that contain the actual field definitions, types, descriptions, modules, etc. This metadata may not always be 100% accurate, or could be lacking details and sufficient explanations.
Be Selective
This section is meant as a guide only. Do NOT copy/paste the entire collection of settings into your CAS configuration; rather pick only the properties that you need. Do NOT enable settings unless you are certain of their purpose and do NOT copy settings into your configuration only to keep them as reference. All these ideas lead to upgrade headaches, maintenance nightmares and premature aging.
YAGNI
Note that for nearly ALL use cases, declaring and configuring properties listed here is sufficient. You should NOT have to explicitly massage a CAS XML/Java/etc configuration file to design an authentication handler, create attribute release policies, etc. CAS at runtime will auto-configure all required changes for you. If you are unsure about the meaning of a given CAS setting, do NOT turn it on without hesitation. Review the codebase or better yet, ask questions to clarify the intended behavior.
Naming Convention
Property names can be specified in very relaxed terms. For instance cas.someProperty, cas.some-property, cas.some_property are all valid names. While all forms are accepted by CAS, there are certain components (in CAS and other frameworks used) whose activation at runtime is conditional on a property value, where this property is required to have been specified in CAS configuration using kebab case. This is both true for properties that are owned by CAS as well as those that might be presented to the system via an external library or framework such as Spring Boot, etc. When possible, properties should be stored in
lower-case kebab format, such as cas.property-name=value.S ettings and properties that are controlled by the CAS platform directly always begin with the prefix cas. All other settings are controlled and provided to CAS via other underlying frameworks and may have their own schemas and syntax. BE CAREFUL with the distinction. Unrecognized properties are rejected by CAS and/or frameworks upon which CAS depends. This means if you somehow misspell a property definition or fail to adhere to the dot-notation syntax and such, your setting is entirely refused by CAS and likely the feature it controls will never be activated in the way you intend.
Validation
Configuration properties are automatically validated on CAS startup to report issues with configuration binding, specially if defined CAS settings cannot be recognized or validated by the configuration schema. The validation process is on by default and can be skipped on startup using a special system property SKIP_CONFIG_VALIDATION that should be set to true. Additional validation processes are also handled via Configuration Metadata and property migrations applied automatically on startup by Spring Boot and family.
Indexed Settings
CAS settings able to accept multiple values are typically documented with an index, such as cas.some.setting[0]=value. The index [0] is meant to be incremented by the adopter to allow for distinct multiple configuration blocks.
REST Protocol Credential Extraction
In the event that the CAS REST Protocol is turned on, a
special credential extractor is injected into the REST authentication engine in order
to recognize credentials and authenticate them as part of the REST request.
The expected parameter name in the request body is passcode that can be found from
Duo Security’s mobile application or received via SMS.
Troubleshooting
To enable additional logging, configure the log4j configuration file to add the following levels:
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...
<Logger name="com.duosecurity" level="debug" additivity="false">
<AppenderRef ref="console"/>
<AppenderRef ref="file"/>
</Logger>
...
You should also use NTP to ensure that your CAS server’s time is correct. Furthermore, CAS typically communicates with Duo’s service on TCP port 443. Firewall configurations that restrict outbound access to Duo’s service with rules using destination IP addresses or IP address ranges are not recommended per Duo Security, since these may change over time to maintain our service’s high availability.